Fuels From Crude Oil

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what is crude oil?
Crude oil is a mixture of compounds called hydrocarbons. Many useful materials can be produced from crude oil. It can be separated into different fractions using fractional distillation, and some of these can be used as fuels. Unfortunately, there are environmental consequences when fossil fuels such as crude oil and its products are used.

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Hydrocarbons

Most of the compounds in crude oil are hydrocarbons. This means that they only contain hydrogen and carbon atoms, joined together by chemical bonds. There are different types of hydrocarbon, but most of the ones in crude oil are alkanes.

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Alkanes

The alkanes are a family of hydrocarbons that share the same general formula. This is:

CnH2n+2

The general formula means that the number of hydrogen atoms in an alkane is double the number of carbon atoms, plus two. For example, methane is CH4 and ethane is C2H6. Alkane molecules can be represented by displayed formulae in which each atom is shown as its symbol (C or H) and the chemical bonds between them by a straight line.

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Alkenes

These compounds are similar to alkanes, in that they can be straight or branched aliphatic hydrocarbons. The only difference is that the alkenes (also known as olefins) contain a carbon-carbon double bond, and have the general formula C 2 H 2n . ...

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Distillation

Distillation is a process that can be used to separate a pure liquid from a mixture of liquids. It works when the liquids have different boiling points. Distillation is commonly used to separate ethanol (the alcohol in alcoholic drinks) from water.
heating → evaporating → cooling → condensing

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Fractional distillation

Fractional distillation differs from distillation only in that it separates a mixture into a number of different parts, called fractions.

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Fractional distillation of crude oil

Because they have different boiling points, the substances in crude oil can be separated using fractional distillation. The crude oil is evaporated and its vapours allowed to condense at different temperatures in the fractionating column. Each fraction contains hydrocarbon molecules with a similar number of carbon atoms.

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Oil fractions

http://www.bbc.co.uk/schools/gcsebitesize/science/images/5_fractional_distillation.gif

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Complete combustion

Fuels burn when they react with oxygen in the air. The hydrogen in hydrocarbons is oxidised to water (remember that water, H2O, is an oxide of hydrogen). If there is plenty of air, we get complete combustion and the carbon in hydrocarbons is oxidised to carbon dioxide:

hydrocarbon + oxygen → water + carbon dioxide

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Incomplete combustion

If there is insufficient air for complete combustion, we get incomplete combustion instead. The hydrogen is still oxidised to water, but instead of carbon dioxide we get carbon monoxide. Particles of carbon, seen as soot or smoke, are also released.